1. Field of Invention
The present invention relates to III-nitride semiconductor light emitting devices.
2. Description of Related Art
Semiconductor light-emitting devices including light emitting diodes (LEDs) are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III–V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. Sapphire is often used as the growth substrate due to its wide commercial availability and relative ease of use. The stack grown on the growth substrate typically includes one or more n-type layers doped with, for example, Si, formed over the substrate, a light emitting or active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region.
Since sapphire is not conductive, contacts to both the p- and n-sides of the active region must be formed on the top side of the device, requiring that a portion of the active region and p-type region be etched away to expose a portion of the buried n-type region. The device is thus a non-planar surface with narrow insulating blocking layers separating the n- and p-contacts, a geometry that is difficult to package. Also, much of the area of the active region is lost to the n-contact and insulating regions, providing a poor fill factor.
U.S. Pat. No. 6,280,523 describes a III-nitride device formed by removing the growth substrate. The epitaxial stack is wafer bonded to a host substrate of GaP, GaAs, InP, or Si. The growth substrate is then removed by laser melting, wet chemical etching, or selective etching of a sacrificial layer. Removing the growth substrate permits the active region to be disposed between two dielectric distributed Bragg reflectors, in order to form a resonant cavity device. The use of a resonant cavity may increase control of the direction of emitted light, increase the amount of light extracted from the device, and increase the spectral purity of the light emitted normal to the device.
Needed in the art are improved III-nitride resonant cavity structures.